Process of recovering water-insoluble lower fatty acid esters of cellulose



Patented July 7, 1942 PROCESS .OFv RECOVERING WATER-INSOLU- BLE LOWER FATTY ACID ESTERS CELLULOSE Charles R. Ford yce and Joseph Gail Stampfli, Rochester, N. Y., assignors to Eastman Kodak Company, Rochesten N. Y., a corporation of New Jersey N Drawing. Application March 10, 1939, Serial No. 261,101

9 Claims.

This invention has to do with the.recovery of filmscrap, having a cellulose derivativebase, in which the scrap is, treated at an elevated temperature with water containing a cation. active detergent.

The treatment of film scrap to remove foreign materials present, such as surface coatings or photographic emulsion layers, is an important task in the photographic industry, but a difiicult one. The objectionable layers of emulsion and subbing must be removed from the film base so that the final recovered film will form a clear solution in solvents therefor. Ordinarily, a long varied and expensive set of treatments is required to recover film scrap without giving, uniformly good results. For instance, usually, one treatment is necessary to take 01f the emulsion, another to remove portions of the subbing, which involves the use of organic solvents, and sometimes a third treatment; to eliminate the last of the subbing. In recovering film scrap, it is desirable to employ as few types of. treatment as possible and to recover the'scrap without the use of organic solvents.

One object of our invention is to remove the foreign materials from scrap photographic film, having a cellulose derivative base, in a simple but yet efiective operation. Another object of our invention is to provide a method for recoverin film scrap in which the use of organic solvents is not necessary. Other objects of our invention will appear herein.

We have found that, if film scrap, preferably in a comminuted condition, is treated with hot water, containing a cation active detergent, the subbing layers and the photographic emulsion layers are substantially, completely removed leaving only the cellulose derivative material, which was employed as the film base.

Almost all photographic film comprises a base of; a cellulose derivative, preferably a cellulose ester, such as cellulose nitrate, cellulose acetate or a mixed ester of cellulose, such as cellulose acetate propionate. or cellulose acetate butyrate, overcoated with a gelatin layer containing a silver halide. Usually it is difiicult to apply the gelatin layer directly to the film base, due to itslack of adherence thereto; consequently one or more intermediate bonding layers are usually necessary to cause good adherence between the photographic. emulsion and the base. Sometimes layers, such as of gelatin or a thin layer of a cellulose derivative, to prevent curling or halation, or a photosensitive layer are present on the back of the film base. renovating the film scrap to recover the cellulose derivative used as the base, it is desirable to remove substantially all of the coatings which have been applied thereto. It is to the substantially, complete removal of these layers, additional to the film base, that our invention is directed.

In carrying out our invention, it is preferred to first comminute the scrap, such as by chopping, although in some cases, such as with wide rolls of scrap film, it might be desirable to run a continuous process, by passing the sheeting through the recovery bath. In the case of the comminuted film, it is stirred with one or more changes of a solution of. a cation active detergent in water at an elevated. temperature after which the recovered film, base is rinsed and dried. The resulting product forms a, smooth, clear solution incoating solvents, which is a satisfactory indication of the, completeness of removal of the overcoatings, such as the gelatin layers and the subbing layers. which are present. The subbing layers, which are susceptible to removalfrom the film in accordance with our invention, are any of the usual types of layers which are used to cause the gelatin layer to adhere to the film base. If the subbing layer is so moisture resistant that it will not be efiected by the solution of a cation active detergent at elevated temperature, it is not suitable to bond withthe gelatin layer.

As the solution of the cation active detergent is susceptible to reuse several times, our film scrap recovery process permits of operation by what might be termed a counter-current system, the scrap first being treated in the most used renovating liquid the succeeding baths being progressively less used and in the final treatment a fresh solution of the cation active detergent in Water is employed. The sole criterion, as to the extent of reuse to which a water solution of a cation active detergent may be put, is that there is still enough detergent present to be effective and the Water does not contain so much gelatin or other contaminating materials that the scrap is not affected or is affected adversely. By using a counter-current system, in which the scrap is treated with a fresh solution of detergent in the final operation any concern regarding the possible efiect produced by the reused liquids is eliminated. The counter-current treatment is carried out by advancing the scrap from one bath to another, each succeeding bath having been less used than the one preceding it.

Although the range of proportion of liquid to film is quite wide, the most suitable for general use is 2051. With this proportion, there is a large excess of liquid to facilitate stirring and yet there is not so great an excess that it is wasteful of solution or of space. If economy is not a consideration, a greater proportion of liquid may be used, such as up to 25, 30, 40 or more parts of liquid to one of film. For apparatus containing an ordinary stirrer at least fifteen parts of liquid to one part of scrap is desirable to assure good soaking. If, however, a different type of agitation, such as tumbling, is used, lower ratios, such as :1 or even 5:1 of liquid to scrap could be used. This operation would preferably be followed by a washing treatment with plain water or some type of flushing operation. Thus, the most economical limits for the ratio of liquid to film scrap is considered as 5-20 parts of detergent solution to one part of film scrap.

The preferred temperature of operation is 180-210" F. This temperature permits the use of the greatest amount of heat under normal pressure conditions. If, however, elevated pressures are not objectionable, the temperature may be raised above the boiling temperature of the water, the maximum temperature permissible being governed by the temperature which the film will stand without decomposing or being effected detrimentally. Although 180 F. isv preferred, as the lower limit, as only a short time is necessary for treating the film scrap, nevertheless, lower temperatures, such as from 180 down to 120 F., might be employed if sufiicient time is given for the treatment. To illustrate the effectiveness of the temperatures near the boiling temperature of water, a time of five minutes for each treatment is sufficient for a temperature of 210 and for the preferred temperature of 180-210 5-20 minutes is satisfactory for each treatment, especially where a plurality of treatments is given as is usually the case. For a lower temperature, such as 160 F., a. total treatment time of 24 hours is desirable to give a substantially complete removal of the foreign material. 7

The cation active detergent may be present in the water from .01% up to 25% or more, the higher limit being set only by the proportion of detergent which can be incorporated. In other words, very low concentrations of the detergent have been found to be effective and yet high concentrations have also given satisfactory results. However, in order to assure reuse of the liquid and economy of operation, it is preferred that the detergent be present in a proportion of .05%2%. In reusing the liquid, especially in cases of extended reuse, the liquid should be fortified at intervals by the further addition of small amounts of detergent. As pointed out previously, it is desirable, especially in case of comminuted scrap, to employ stirring as this uniformly exposes the particles of scrap to the action of the liquid and thereby gives a better treatment than would be possible where stirring is not employed.

With scrap filni having no silver halide layer, such as waste material from the subbing operations, one treatment is sufficient to recover the ester employed as the film base. In the case of film scrap having photographic emulsion thereon, one treatment substantially removes all the foreign materials, but to obtain an excellent recovered product it is desirable to use more than one treatment. Twotreatments give a fairly satisfactory product and three are ordinarily sufficient to give a product of high quality. Further treatments may be given if desired but are ordinarily unnecessary.

Some of the subbing layers which might be present and which are removable by our process are gelatin layers, whether hardened or not, layers of polyvinyl acetate (common known as Gelva resin), nitrate subbing layers, layers of resins, such as glyptal resins or mixtures of materials such as cellulose nitrate-gelatin or gelatin-oxidized cellulose acetate sub. Ordinarily the subbing layer, except in the case of gelatin, is exceedingly thin, not exceeding one tenthousandth of an inch. If a film scrap should be unusual in having uncommonly thick subbing or backing layers thereon, it might be desirable to employ an auxiliary treatment after our recovery operation, such as by washing the scrap with a liquid which is a solvent for the heavy layer, and a non-solvent for the film base. At the present time, however, this practice is believed to be quite unnecessary.

The cation active detergents, which are suitable for use in our process, are those of a watersoluble variety which have been previously mentioned in the prior art. For instance, the watersoluble cation active detergents, disclosed in U. S. Patent No. 2,125,031 of Polak et al., are admirably suited for the purposes of our invention. Some of the compounds of this type, which give a good product when used in accordance with our invention, are triethyllaurylammonium bromide, triethyllaurylammonium perchlorate, lauryl pyridinium p-toluene-sulfonate, and dimethylbenzylcetylammonium chloride. Instead of the halides, the salts of other acids, giving water-soluble products, such as the sulfates, may be employed. An example of compounds, which are valuable in our process, are the quaternary ammonium salts having the following formula:

R3-NX in which R represents aliphatic or aralkyl radicals, R represents aliphatic radicals, having 8 or more carbon atoms, and X represents an acid radical, giving water-soluble salts with the quaternary ammonium base. The following examples describe processes which embody our invention:

Example I 30 parts of film scrap, having a base of a lower fatty acid ester of cellulose, were chopped up and then boiled for one hour with 600 parts of a 0.5% solution of dimethyl benzyl cetyl ammonium chloride in water withoccasional agitation. The mother liquor was removed and the treatments were repeated twice, making a total of three treatments. The scrap was rinsed by boiling 6-8 times for fifteen minutes, each time with 600 parts of distilled water, and dried. The product gave a smooth, clear, brilliant solution in coating solvents, indicating complete removal of foreign materials known to be present in the untreated film scrap.

Example II 40 parts of chopped processed film was boiled for three periods of one hour each with 600 parts of a 0.25% solution of dimethyl benzyl cetyl ammonium chloride. The scrap was rinsed, as in Example I, and dried. A solution of it in coating solvents was smooth and clear.

Example III 30 parts of chopped film scrap was given 3 one hour boils with 600 parts of a 0.05% solution of dimethyl benzyl cetyl ammonium chloride in distilled water, rinsed, as in Example I, and dried. The product formed a grain-free solution in coating solvents.

Example IV 30 parts of chopped film scrap was boiled with three successive portions of 600 parts each of a 1% solution of triethyllaurylammonium perchlorate in distilled water. The product was rinsed, as in Example I, and dried. It formed a smooth solution in coating solvents.

In our process, it is preferred that a purified water be employed, as we have found that certain impurities in some types of water used in the boiling operations either decrease or completely destroy the effectiveness of our treatment. Therefore, it is essential in our process that a purified water, such as distilled or softened water, be used, or that the solution have a pH sufficiently acid to neutralize the effect of the water.

The cellulose esters, recovered by our process, may be dissolved up in suitable coating solvents and used to form sheeting, or coatings, or any other purpose for which the use of a clear solution of a cellulose ester is desirable.

We claim:

1. A method of renovating film scrap, having a base of a water-insoluble cellulose compound which comprises treating the scrap with a plurality of 0.5% solutions of dimethyl benzyl cetyl ammonium chloride in water, at a temperature above 120 F. but below the decomposition temperature of the film base until a surface coating is removed therefrom.

2. A method of renovating film scrap, having a base of a water-insoluble cellulose compound which comprises treating the scrap with a plurality of 1% solutions of triethyllaurylammonium perchlorate at a temperature above 120 F. but below the decomposition temperature of the film base until a surface coating is removed therefrom.

3. A method of removing a thin layer of nitrocellulose from a base of a water-insoluble lower fatty acid ester of cellulose to which the layer is attached, which comprises treating the cellulose ester material with a bath substantially free of alkali essentially consisting of a water solution of a water-soluble cation active detergent in which a negative substituent is linked directely to nitrogen, the cation portion of the detergent containing an alkyl substituent having at least 8 carbon atoms, at a temperature above 120 F. but below the decomposition temperature of the fatty acid ester of cellulose until the thin nitrocellulose layer is removed therefrom.

4. A method of removing a thin layer of nitrocellulose from a base of a water-insoluble lower fatty acid ester of cellulose to which the layer is attached, which comprises treating the cellulose ester material with a bath substantially free of alkali essentially consisting of water containing 0.05 to 2% of a cation active detergent in which a negative substituent is linked directly to nitrogen, the cation portion of the detergent containing an alkyl substituent having at least 8 carbon atoms, at a temperature of 180-210 F. until the thin nitrocellulose layer is removed from the base material.

5. A method of renovating film scrap, having a base of a water-insoluble lower fatty acid ester of cellulose and a subbing layer of nitrocellulose thereon, which comprises treating the scrap With a bath substantially free of alkali essentially consisting of a water solution of a water-soluble cation active detergent in which the negative substituent is linked directly to nitrogen, the cation portion of the detergent containing an alkyl substituent having at least 8 carbon atoms, at a temperature above F. but below the decomposition temperature of the film base until the nitrate subbing layer is removed therefrom.

6. A method of renovating film scrap having a base of a water-insoluble lower fatty acid ester of cellulose and a nitrocellulose subbing layer thereon, which comprises treating the scrap with a plurality of water solutions of a cation active detergent in water, at a temperature above 120 F. but below the decomposition temperature of the film base until the nitrate subbing layer is removed therefrom, the cation active detergent employed having a negative substituent linked directly to nitrogen and the cation portion of the detergent containing an alkyl substituent of at least 8 carbon atoms.

'7. A method of renovating film scrap having a base of a water-insoluble mixed ester of cellulose the acyl of which consists of fatty acid groups of 2-4 carbon atoms to Which is attached a thin layer of nitrocellulose, which comprises treating the scrap with an alkali-free bath essentially consisting of a water solution of a water-soluble cation active detergent in which the negative substituent is linked directly to nitrogen, the cation portion of the detergent containing an alkyl substituent having at least 8 carbon atoms, at a temperature above 120 F. but below the decomposi tion temperature of the film base until the nitrate subbing layer is removed therefrom.

8. A method of renovating film scrap, having a base of a water-insoluble lower fatty acid ester of cellulose and a thin layer of nitrocellulose thereon which comprises treating the scrap with a 0.5% solution of dimethyl benzyl cetyl ammonium chloride in water, at a temperature above 120 F. but below the decomposition temperature of the film base until the thin nitrate layer is removed therefrom.

9. A method of renovating film scrap, having a base of a water-insoluble lower fatty acid ester of cellulose and a thin layer of nitrocellulose thereon which comprises treating the scrap with a 1% solution of triethyllaurylammonium perchlorate, at a temperature above 120 F. but below the decomposition temperature of the film base until the thin nitrate layer is removed therefrom.

CHARLES R. FORDYCE. JOSEPH GAIL STAMPFLI. 

